Electric incandescent halogen lamp with barrel-shaped bulb

ABSTRACT

An electric incandescent lamp (4), in particular an incandescent halogen  p, has a bulb or envelope (5), which is shaped as an ellipsoid or optionally ellipsoidlike (barrel-shaped body) and provided with an IR layer (8). Located inside the bulb (5) axially is a compact filament (2&#39;) of circular-cylindrical outer contour; the focal lines of the ellipsoid-like barrel-shaped body each coincide approximately with the last luminous winding on the two ends of the filament. This improves lamp efficiency. The compact filament is preferably in the form of a helical coil (2&#39;), whose power supply lead (10b) remote from the seal is returned to inside the helical coil (2&#39;), or is shaped like a double helix.

FIELD OF THE INVENTION

The invention relates to an electric incandescent lamp, and moreparticularly to an incandescent halogen lamp having arotation-symmetrical bulb or envelope, and to filaments that aresuitable for such incandescent lamps.

BACKGROUND

Incandescent halogen lamps, both in general lighting and for speciallighting purposes, are often used in combination with a reflector, suchas in projection technology.

The rotationally symmetrical form of the lamp bulb or envelope, combinedwith an infrared-radiation-reflecting coating--hereinafter called an IRlayer for short--applied to the inner and/or outer surface of the bulbhas the effect that a majority of the IR radiation power produced by thefilament is reflected back. The resultant increase in lamp efficiencycan be utilized to increase the temperature of the filament andconsequently the light flux, if the electrical power consumption isconstant. On the other hand, a given light flux can be attained withless electrical power consumption--an advantageous "energy-savingeffect". Another desirable effect of the IR layer is that markedly lessIR radiation power is emitted through the bulb, heating the environment,than in conventional incandescent lamps.

Because of unavoidable absorption losses in the IR layer, the powerdensity of the IR radiation components inside the bulb decreases withthe number of reflections, and consequently the efficiency of theincandescent lamp drops also. It is therefore decisive for the actuallyattainable increase in efficiency to minimize the number of reflectionsrequired to return the individual IR rays to the filament.

This type of lamp is disclosed for instance in U.S. Pat. No.4,160,929Thorington et al., European Patent EP A 0 470 496, and GermanPatent Disclosure DE-OS 30 35 068. U.S. Pat. No. 4,160,929 teaches thatto optimize lamp efficiency, the geometric shape of the filament must beadapted to that of the bulb. Moreover, the filament must be positionedas exactly as possible in the optical center of the bulb.

As a result, a wave front originating at the surface of the filament isreflected back, unimpeded, by the bulb surface. Aberration losses areconsequently minimized. A spherical bulb, for instance, should in anideal case have a centrally located and likewise spherical filament.Because of the limited ductility of the tungsten wire that is used as arule, however, coil shapes for this purpose are attainable only to agreatly limited extent. A cubelike coil has been proposed as a rough butpractical approximation for a sphere. In another embodiment, the coilhas its largest diameter in its middle. That diameter decreasessuccessively toward the two ends of the coil. For an ellipsoid bulbshape, it has been proposed that one filament be located at each of thetwo focal points of the ellipsoid.

EP A 0 470 496 discloses a lamp with a spherical bulb, with acylindrical filament located in the center. This reference teaches thatthe losses of efficiency from the deviation of the filament from theideal spherical shape can be kept acceptably low on the followingpreconditions. Either the bulb diameter and filament diameter or lengthmust be adapted carefully to one another within a tolerance range, orthe diameter of the filament must be markedly less (less than a factorof 0.05) than that of the bulb. A lamp with an ellipsoid bulb in whosefocal line an elongated filament is axially arranged is also disclosed.

German Patent Disclosure DE-OS 30 35 068 provides teaching for the sakeof minimizing the aberration losses, which even in the last embodimentabove are unavoidable. In this disclosure, the two focal points of theellipsoid bulb are located on the axis of the cylindrical filament andat predetermined distances from its respective ends.

THE INVENTION

The object of the invention is to overcome the disadvantages mentionedand to disclose an incandescent lamp that excels in having an efficientreturn of the emitted IR radiation to the filament and consequently highefficiency. Moreover, compact lamp dimensions at high radiant densitiesor luminance are to be attained, as sought particularly for low-voltageincandescent halogen lamps.

A further object is to disclose an especially compact design of thefilament, which is suitable in particular but not exclusively for lampsaccording to the invention.

Briefly, the fundamental concept of the invention is based on shapingthe rotationally symmetrical bulb wall in such a way that nearly all theIR rays that are generated on the jacket face of a filament ofsubstantially circular-cylindrical outer shape located axially insidethe bulb will return to the filament after being reflected from the bulbwall.

The bulb surface substantially corresponds to an ellipsoidlikebarrel-shaped body and is generated by the rotation of an ellipticalportion, or only approximated elliptical portion. The axis of rotationis located in the plane of the elliptical portion and is shiftedparallel by some distance from the long half-axis thereof. As a result,the two focal points of the elliptical portion each describe an annularfocal line.

In a preferred embodiment, the spacing, or shift, of the axis ofrotation is approximately equivalent to the radius of the approximatelycircular-cylindrical envelope curve of the filament. The length of thefilament is approximately equivalent to the spacing of the two focallines, or may deviate from that slightly. As a result, the two annularfocal lines of the barrel-shaped body each approximately coincide withthe last luminous winding on the two ends of the filament.

Axially arranged single or double coils of tungsten are used for thefilament. The geometrical dimensioning or in other words the dimension,pitch and length depends, among other factors, on the desired electricalresistance R of the coil, which in turn depends on the desiredelectrical power consumption P for a given supply voltage U. BecauseP=U² /R, the coils in high-voltage (HV) lamps are as a rule longer thanin low-voltage (LV) types.

The filament is electrically conductively connected to two power supplyleads, which are extended to the outside in gas-tight fashion and arelocated either both on one end of the bulb, or are located separately onthe two opposed ends of the bulb. The sealing is generally effected viaa pinch. Some other sealing technique, such as fusing in of a plate, isalso possible. The version which is closed on one end is especiallysuitable for LV applications. In that case, because of the relativelyshort filament, very compact lamp dimensions are attained. In the caseof the comparatively long and as a rule less rigid coils for HVapplications, it may be advantageous to support the filament with anaxially arranged retaining device of electrically insulatingheat-resistant material, as has been proposed for instance in GermanUtility Model DE-GM 91 15 714. In the case of bulbs closed on both ends,this feature may be dispensed with under some circumstances, because inthat case the coil can be fixed on both ends by means of a respectivesubstantially rigid, axially arranged power supply lead.

To optimize lamp efficiency, it is advantageous if as large as possiblea portion of the bulb wall can be used as an effective reflectionsurface. This can be attained in particular by providing that on one oroptionally both ends, the lamp bulb has a neck in the region of thepower leadthrough. The neck surrounds the power leadthrough as closelyas possible and merges with a seal. To enable inserting the filamentinto the bulb through the neck during manufacture of the lamp, the innerdiameter z of the lamp neck must be somewhat larger, optionally on atleast one end of the bulb, than the outer diameter d of the filament.Typical values for the difference between the two diameters are up to 5mm, but preferably less than 2 mm. If D is the largest outer diameterperpendicular to the rotary axis of the bulb, then the overallrelationship is d<z<D. Tests have shown that the lamp of the inventioncan be operated with good efficiency and compact dimensions as long asthe quotient d/D of the outer diameter d of the filament and the largestouter diameter D of the bulb is greater than approximately 0.15, and ispreferably in the range between greater than 0.15 and less than 0.5, andthe quotient d/z of the outer diameter d of the filament and the innerdiameter z of at least one neck is greater than approximately 0.25,preferably greater than or equal to 0.4.

The fundamental relationships can be explained especially simply withthe aid of the schematic longitudinal section shown in FIG. 1 through alamp bulb. For the sake of simplicity, the bulb is shown as a closedellipsoid barrel-shaped body 1 of negligible wall thickness, in whoseinterior a filament 2 of circular-cylindrical outer contour is centrallyaxially arranged. The power supply leads and the pinch (or pinches) arenot shown, for the sake of simplicity. The longitudinal axis r of thefilament 2 forms the rotary axis of the barrel-shaped body 1. Theportion of the barrel-shaped body that is immediately adjacent to thejacket face of the filament is generated by an ellipse half 3. The fourcorners of the rectangular longitudinal section of the filament areidentical to the focal points F₁, F₂, F₁ ', F₂ ' of the two opposedellipse halves 3, 3' of the contour of this bulb portion. Because of therotational symmetry, the two focal points of the generating ellipse halfdescribe two corresponding circular focal lines f₁ and f₂, respectively,which coincide with the two circular edges of the outer contour of thecircular-cylindrical filament. The maximum spacing between the jacketface of the filament and the bulb wall is accordingly equivalent to theshort half-axis b of the ellipse half that generates the partial bulbcontour.

DEFINITION

The term "barrel-shaped" used herein and in the claims thus refers to abody of rotation which, in cross section, in a plane parallel to acentral axis r (FIG. 1) and at any angle about this central axis, iselliptical, with the focal points of the ellipse offset (d/2, FIG. 1)from the central axis r. The circumference of this body, thus, isgenerated by a half ellipse in which the focal points, themselves,rotate or nutate, in a circle of radius d/2 about the central axis r.

The foregoing definition clearly contrasts a "barrel-shaped body", asdefined, from an ellipsoid which is generated by a single ellipse (orhalf ellipse), whose focal points are fixed and on the axis of rotation.

The decisive advantage over previous solutions is that now all the raysthat originate at the outer circumferential, i.e. the jacket face orgenerated surface, return to this generated surface, or face after asingle reflection at the bulb wall. This is shown as an example for thetwo arbitrarily selected rays F₁ AF₂ and P₁ AP₂. The reason is that allthe rays that originate somewhere along the connecting line F₁ F₂between the two focal points F₁, F₂ are reflected at a smaller anglefrom plumb, at point A of the ellipse half 3, than the correspondingfocal point rays. Because of the rotational symmetry, this is true forall the rays that originate at the outer surface of the filament andextend in the planes that intersect at the rotary axis (that is, thelongitudinal axis r of the bulb).

For the rays that extend in the planes at right angles to the rotaryaxis, the contours of the bulb and the filament each correspond tocircles concentric with one another. Approximately circular wavestherefore form in these planes, and their wave fronts are adapted to thecorresponding bulb contour and are consequently reflected back againunimpeded.

The geometrical dimensioning of the coil, especially its length L andits diameter d, is calculated substantially from the electrical powerconsumption contemplated. With the aid of the ellipse equation (see forexample McGraw-Hill Encyclopedia of Science, Page 560), a relationshipcan thus be given for the long half-axis a of the ellipse half (orelliptical portion) that generates the ellipsoid portion of thebarrel-shaped body: ##EQU1##

In this illustration, the short half-axis b and thus the largestdiameter D=2·(b+d/2) of the bulb are a "freely" selectable parameter.That is, while preserving the fundamental reflection relationshipsdescribed, different kinds of compact bulbs can be achieved.

In a first embodiment, the IR layer is applied to the inner surface ofthe bulb. According to the above teaching, this inner surface is shapedas an approximately optimal reflection surface for the IR raysoriginating at the jacket face of the filament. However, during themanufacture of the bulb, the shaping of the inner surface cannotgenerally be monitored as exactly as is possible for the outer face--forinstance by means of suitable forming rollers. As a result, the IRlayers does not generally have exactly the calculated contour. Moreover,in this case the material of the coating must be resistant to the fill.

In a second embodiment, the IR layer is located on the outer surface ofthe bulb, so there is no need to take the fill into consideration.Moreover, the IR layer is simple to apply in that case. However, now theIR rays originating at the jacket face of the filament are broken at theboundary face between the medium inside the bulb and the medium of thebulb wall. The resultant offset of the rays means that--depending on thewall thickness and the difference in index of refraction at the boundaryface--some rays, and especially those that originate at the focalpoints, are no longer reflected back into the focal line. To optimizelamp efficiency, it is therefore advantageous to compensate for thisoffset of rays by means of a suitably adapted bulb contour. In thiscase, the generatrix is a slightly modified elliptical portion (notshown), which must be calculated numerically. The peripheral conditionis again that all the rays that originate at the jacket face of thefilament and extend in the planes that intersect in the rotary axis(i.e., the longitudinal axis of the bulb) return to the jacket faceagain after being reflected once at the IR layer.

In a preferred embodiment with a bulb closed on one end, the innerdiameter of the neck is only insignificantly larger than the outerdiameter of the filament. For this reason, especially when the bulb isclosed by a pinch seal that is relatively wide to allow the foils topass through, the bulb has a pronounced constriction in the region ofthe neck. As a result, an especially large effective reflection surfacearea of the overall bulb and consequently correspondingly highefficiency are attained. For this purpose, an especially compact designof the power supply leads and of the filament have been developed. Thepower supply leads are extended inside the outer diameter of thefilament, from the seal to the ends of the filament. In one embodiment,the power supply lead connection to the end of the filament remote fromthe seal is returned to inside the filament, preferably centrally andaxially. This prevents shading of the coiled surface. An especiallycompact arrangement is a double helix-like coil structure. The filamentthen comprises two coil segments that mesh with one anotherthree-dimensionally. In one embodiment, the two coil segments areembodied as identical helical lines. These lines are arranged such thattheir two longitudinal axes coincide and are offset from one anotheraxially by approximately one-half the pitch height. The pitch height isdefined here as the distance within which the helical lines execute onecomplete turn. The two coil segments are joined together on the firstend of the filament. On the opposite end of the filament, the two coilsegments each merge with a respective power supply lead.

These compact filament forms can be used not only in barrel-shapedbodies but also in other shapes of bulbs, such as ellipsoid or sphericalbulbs, as has been noted at the outset.

Advantageously, the pitch of the coiling of the filament is as small aspossible, so that the IR rays reflected by the bulb will be highlylikely to strike the filament.

This kind of compact design of the filament can be achieved especiallyeasily in LV lamps, because in them the thickness of the coil wire isespecially great. Thus, short filaments of high rigidity can beproduced, in accordance with the above-described embodiments.

The compact geometrical dimensions predestine this lamp especially forcombination with an external reflector, such as that used in protectiontechnology. The optical system efficiency is in fact higher, the betterthe light source used approximates an ideal point-type light source.

To reinforce centering of the filaments, in one variant at least one ofthe two power supply leads of the filament is spread apart, in thedirection of its end remote from the filament, to a spacing greater thanthe inside diameter z of the lamp neck. The spreading is effected overthe entire length, or only over a portion of the respective power supplylead. Preferably, both power supply leads have the same degree ofspreading symmetrically to the longitudinal axis of the filament. Whenthe filament is inserted into the bulb, the ends of the power supplyleads remote from the filament are braced against the inner wall of theneck of the lamp and thus bring about forced centering of the filamentinside the bulb in one plane.

The bulb is typically filled with inert gas, such as N₂, Xe, Ar and/orKr. In particular, it contains halogen additives that maintain atungsten-halogen cycle process, to counteract blackening of the bulb.The bulb comprises a light transmissive material, such as quartz glass.

The lamp may be operated with an outer bulb. If an especially strongreduction of the IR capacity projected into the environment is desired,then the outer bulb may also have an IR layer.

The IR layer for instance may be in the form of an interference filterknown per se--typically, a succession of alternating dielectric layerswith different indexes of refraction. The basic layout of suitable IRlayers is described for instance in EP A 0 470 496.

DRAWINGS

The invention will be described in further detail below in terms ofseveral exemplary embodiments. Shown are in:

FIG. 1, the basic principle of the invention, illustrated by alongitudinal section through an ellipsoid barrel-shaped body;

FIG. 2, an exemplary embodiment of an LV lamp, pinched on one end, withcoating on the outside;

FIG. 3, an exemplary embodiment of an LV lamp, pinched on one end, withcoating on the inside;

FIG. 4, an exemplary embodiment of a HV lamp, pinched on one end, withcoating on the outside;

FIG. 5, an exemplary embodiment of an HV lamp, pinched on both ends,with coating on the outside.

In FIG. 2, a first exemplary embodiment of a lamp 4 according to theinvention is schematically shown. This is an incandescent halogen lampwith a rated voltage of 12 V and a rated output of 75 W. It comprises alamp bulb or envelope 5, pinched on one end, which is shaped as anellipsoidlike barrel-shaped body. It is made of quartz glass with a wallthickness of approximately 1 mm, and on its first end it merges with aneck 9 that ends at a pinch seal 6. On its opposite end, it has a pumptip 7. Applied to its outer surface is an IR layer 8, comprising aninterference filter with more than 20 layers of Ta₂ O₅ and SiO₂. In thisway, an especially dimensionally stable form of the IR layer isattained, since in the manufacture of the bulb 5, the calculated contourof the ellipsoid barrel-shaped body is imposed upon the outer surface ofthe bulb. The largest outer diameter of the bulb 5 is approximately 10mm, and the length of the bulb neck 9 is approximately 3 mm, for anouter diameter of about 6 mm. A fill of approximately 6670 hPa of xenon(Xe), with an admixture of 5600 ppm of hydrogen bromide (HBr), and anaxially arranged filament 2' with a length of 3.7 mm and an outerdiameter of 2.2 mm are all located in the inside of the bulb. The resultis a ratio between the outer diameter of the filament 2' and the innerdiameter of the neck 9 of approximately 0.7. The ratio between the outerdiameter of the filament 2' and the largest outer diameter of the bulb 5is approximately 0.22. The geometry of the filament 2' and the contourof the bulb 5 are adapted to one another in such a way that the lastturn of each of the two ends of the wound or coiled filament 2' isnearly identical with the focal lines of the inside of the bulb 5, seelines f₁, f₂ of FIG. 1.

The filament 2' is made from tungsten wire, with a diameter of 227 μmand a length of 94 mm; at room temperature, its electrical resistance isapproximately 0.09 Ω. The tungsten wire is wound into a single helicalcoil, which has eleven turns with a pitch of 316 μm and a core diameterof 1746 μm, corresponding to a pitch factor of about 1.39 and a corefactor of about 7.7.

The power supply leads 10a, 10b are formed directly by the coil wire andare joined to molybdenum foils 11a, 11b in the pinch seal 6. Themolybdenum foils 11a, 11b are in turn connected to outer base prongs12a, 12b. The first power supply lead 10a is extended parallel to thelongitudinal axis of the lamp and in alignment with the circumferentialsurface of the filament 2'. The second power supply lead 10b of thefilament 2' is bent toward the axis and extends centrally along the axisof the windings to the end remote from the base. In this way, anyshading thereby is prevented.

The lamp has a color temperature of approximately 3150 K. The light fluxis 2100 lm, corresponding to a light yield of 28.7 lm/W. In comparisonto operation of the same lamp without an IR layer, up to 25% of theelectrical energy can be saved.

FIG. 3 shows a second exemplary embodiment of a lamp 4' according to theinvention, in a schematic illustration. In contrast to the firstexemplary embodiment, the IR layer 8' is on the inside of the bulb 5.Unlike the conditions in FIG. 2, the IR rays therefore strike the IRlayer directly, without first passing through the wall of the bulb 5.Consequently, there is no ray offset from refraction. The axiallycentrally arranged, singly coiled filament 13 is shaped in the manner ofa double helix directly from a 227-μm-thick tungsten wire. One half ofthe coiling of the coil body is extended in the direction of the pumptip 7, in the manner of a clockwise screw. The second half is coiled inthe same direction of rotation but in the opposite longitudinaldirection. The two power supply leads 10a, 10b are formed directly bythe ends of the coil wire. They are located in the plane of the pinchseal 6 and are guided parallel to one another--approximately at thespacing of the diameter of the filament coil--in each case from the endnear the base of the filament toward the molybdenum foils 11a, bconnected to the base pins 12a, b. If the fill comprises 6670 hPa ofxenon (Xe) with an admixture of 5600 ppm of hydrogen bromide (HBr), thenup to 30% of the energy can be saved, compared to operation of the samelamp without a coating.

In FIG. 4, a further exemplary embodiment of a lamp 4" is schematicallyshown. This is an HV incandescent halogen lamp, pinched on one end andwith coating 8 on the outside, which is suitable for direct operation ata mains voltage of 230 V. The doubly coiled filament 14 comprises 18helical winding turns. The turns are wound onto an electricallyinsulating tube 15 of Al₂ O₃ ceramic, which assures good mechanical andthermal stability. This is of great importance for optimal efficiency ofthis lamp 4", because only in this way can the jacket face of thefilament 14 be fixed with the requisite accuracy between the two focallines of the bulb 16. This is particularly true when the lamp 4" isoperated in a horizontal position. In that case, the tube 15 preventssagging of the long, not very rigid filament 14. The end of the filament14 remote from the seal is electrically conductively connected to theinternal return 17 via a tungsten hoop 171. Because of the support ofthe internal return 17 in the pump tip 18, the filament 14 is axiallycentered. This type of retaining a filament is well known, andillustrated, for example, in DE-GM 91 15 714, assigned to the assigneeof this application.

In FIG. 5, a further exemplary embodiment of a lamp 4"' is schematicallyshown. This is an HV incandescent halogen lamp, pinched on both ends andwith coating 8 on the outside, which is suitable for direct operation ata mains voltage of 120 V. Inside the bulb 19, a singly coiled filament20 is arranged concentrically; as in the previous examples, the lastwinding of each of the two ends of the filament 20 are nearly identicalwith the focal lines of the bulb 19. The filament 20 is retained bymeans of two axially arranged power supply leads 22a, 22b. Between thebulb 19 and each of the two pinches 21a, 21b, the lamp 4"' has arespective neck 23a and 23b. The inside diameter of the first neck 23ais only insignificantly larger than the outer diameter of the filament20. During production, the filament 20 is inserted through this neck 23ainto the bulb 19. The inside diameter of the oppositely located neck 23bis only insignificantly greater than the diameter of the power supplylead 22b that it closely surrounds. As a result, the lamp 4"' has alarger reflective surface area on this end than on the end opposite it.When operated vertically, the lamp is preferably oriented such that theend of the lamp that has the narrower neck 23b points downward. In thisway, a temperature gradient caused by convection between the two ends ofthe filament is counteracted.

The invention is not limited to the exemplary embodiments discussed. Inparticular, individual characteristics of different exemplaryembodiments may also be combined with one another.

What is claimed is:
 1. An electric incandescent lamp, optionally anincandescent halogen lamp (4-4"'), havinga rotationally symmetrical bulbor envelope (5, 16, 19), which has a longitudinal axis (r); an infrared(IR) radiation reflecting layer (8) on a wall surface of the bulb; and acoiled filament (2, 2', 13, 14, 20) which, when energized, emits visiblelight, located axially in the bulb and retained in the bulb by means oftwo power supply leads (10a, 10b-22a, 22b), characterized in that thebulb (5, 16, 19) forms a barrel-shaped body of rotation of ellipsoid or,optionally, approximately ellipsoid partial contour, which body, incross section, in a plane parallel to a central axis (r) and at an angleabout the central axis, has a generatrix which is elliptical orapproximately elliptical, with the focal points (F1, F2) of the ellipseoffset by a predetermined distance (d2) from the central axis (r), sothat the circumference or contour of this body will be generated by ahalf, at least part-ellipse or approximate ellipse, in which the focalpoints (F1, F2), themselves, rotate or nutate about the central axis (r)to form focal lines (f1, f2) which are circular, or form focal circles,which focal circles have a radius of said predetermined distance (d/2).2. An electric incandescent lamp, optionally an incandescent halogenlamp (4-41'), havinga rotationally symmetrical bulb or envelope (5, 16,19), which has a longitudinal axis (r); an infrared (IR) radiationreflecting layer (8) on a wall surface of the bulb; and a coiledfilament (2, 2', 13, 14, 20) which, when energized, emits visible light,located axially in the bulb and retained in the bulb by means of twopower supply leads (10a, 10b-22a, 22b), characterized in that the bulb(5, 16, 19) forms a barrel-shaped body of rotation of ellipsoid or,optionally, approximately ellipsoid partial contour, which body, incross section, in a plane parallel to a central axis (r) and at an angleabout the central axis, has a generatrix which is elliptical orapproximately elliptical, with the focal points (F1, F2) of the ellipseoffset by a predetermined distance (d2) from the central axis (r), sothat the circumference or contour of this body will be generated by ahalf, at least part-ellipse or approximate ellipse, in which the focalpoints (F1, F2), themselves, rotate or nutate about the central axis (r)to form focal lines (f1, f2) which are circular, or form focal circles,which focal circles have a radius of said predetermined distance (d/2);and in that the axial positions of said two focal lines or circles (f1,f2) of the ellipsoid or, optionally, approximately ellipsoid partialcontour of said barrel-shaped body (1, 5, 15, 19) each coincideapproximately with the last luminous turn on two ends of the coiledfilament (2, 2', 13, 14, 20).
 3. The electric incandescent lamp of claim1, characterized in that the IR-radiation-reflecting layer (8') isapplied to the inner surface of the bulb (5).
 4. The electricincandescent lamp of claim 1, characterized in that the ellipsoid or,optionally, part ellipsoid-like portion of the contour of thebarrel-shaped body (1, 5, 16, 19) is generated by an at leastapproximated elliptical portion (3).
 5. The electric incandescent lampof claim 4, characterized in that the long half-axis of the at leastapproximated elliptical portion is shifted parallel to the longitudinalaxis of the lamp, optionally by approximately the outer radius of thecoiling of the filament (2, 2', 13, 14, 20).
 6. The electricincandescent lamp of claim 5, characterized in that the length of thefilament (2, 2', 13, 14, 20) is approximately equivalent to the spacingof the two focal points of the elliptical portion.
 7. The electricincandescent lamp of claim 1, characterized in that the bulb (5, 16, 19)has at least one neck (9, 23a, 23b) on at least one end, which necksurrounds at least one power supply lead (10, 10b, 22a, 22b) as closelyas possible and is sealed in gas-tight fashion (6, 21a, 21b).
 8. Theelectric incandescent lamp of claim 7, characterized in that thequotient d/D of the outer diameter d of the filament (2', 13, 14, 20)and the largest outer diameter D of the bulb 5, 16, 19) is greater thanapproximately 0.15, and the quotient d/z of the outer diameter d of thefilament (2', 13, 14, 20) and the inner diameter z of the at least oneneck (9, 23a) is greater than approximately 0.25.
 9. The electricincandescent lamp of claim 8, characterized in that the quotient d/z ispreferably greater than or equal to 0.4.
 10. The electric incandescentlamp of claim 8, characterized in that the quotient d/D is preferably inthe range between 0.15 and 0.5.
 11. The electric incandescent lamp ofclaim 1, characterized in that two power supply leads (10a, 10b) areprovided, guided jointly through a neck (9) of the bulb, said powerleads having a spacing that is less than or equal to the outer diameterd of the filament (2', 13).
 12. The electric incandescent lamp of claim1, characterized in that the filament is in the form of a helical coil(2'), and has a power supply lead (10b) remote from a bulb seal, whichis led back to the seal inside the helical coil (2').
 13. The electricincandescent lamp of claim 1, characterized in that the filament (14) isreinforced by an axially located retaining device (15) of electricallyinsulating material positioned within the coiling of the filament. 14.The electric incandescent lamp of claim 1, characterized in that thefilament is shaped as a double helix (13).